JP7167413B2 - Spray drying system and method - Google Patents

Description

[Cross reference to related applications]
[0001] This patent application is subject to U.S. Provisional Patent Application No. 62/578,009, filed Oct. 27, 2017 and U.S. Provisional Patent Application No. 62/658,295, filed Apr. 16, 2018. claim the interests of No. All provisional patent applications referenced above are incorporated by reference.

[0002] This invention relates generally to spray dryers, and more particularly to apparatus and methods for spray drying liquids into dry powder form.

[0003] Spray drying is a well-known and widely used process for spraying a liquid slurry into a drying chamber into which heated air is introduced to dry the liquid into a powder. A slurry typically includes a liquid such as water, an ingredient such as a food, flavor, or pharmaceutical agent, and a carrier. During the drying process, the liquid is driven off, leaving the ingredients in powder form encapsulated within the carrier. Spray drying is also used to produce powders that do not require encapsulation, such as various foods, additives, and chemicals.

[0004] Spray-drying systems are typically relatively large in construction, having drying towers that can reach several stories in height. Not only is the equipment itself a significant capital investment, but the facility in which the equipment is used must be of sufficient size and design to accommodate such equipment. Heating requirements for drying media can also be expensive.

[0005] While it is desirable to use electrostatic spray nozzles to generate charged particles, which promotes more rapid drying, the majority of such spray drying systems are of steel construction. As a result, charged liquids, especially if unintentionally grounded, can charge system components, interfere with the operation of electrical controls, disrupt operation, of liquid may be ejected.

[0006] It is known to form the drying chamber of an electrostatic spray dryer of non-metallic materials to better insulate the system from charged liquids, but particles adhere and accumulate on the walls of the drying chamber. Possible and time-consuming cleaning that interferes with the use of the system. Additionally, very fine dry powders in the heated air atmosphere within the drying chamber can create a hazardous explosive condition through inadvertent sparking or malfunction of electrostatic spray nozzles or other components of the system.

[0007] Such spray drying systems must also be operable to spray dry different forms of liquid slurries. For example, in the flavor industry, it may be necessary to operate the system with a citrus flavoring ingredient in one run, a coffee flavoring ingredient in the next run, and so on. Residual flavoring substances adhering to the walls of the drying chamber can contaminate the taste of subsequently processed products. Naturally, in the field of pharmaceuticals it is imperative that subsequent pharmaceutical runs are free of cross contamination.

[0008] Further, existing spray drying systems lacked easy versatility. It may be desirable to dry smaller lots of product that do not require the use of an entire large drying system. Additionally, it may be desirable to change the manner in which materials are sprayed and dried within the system in certain applications. In still other processes, it may be desirable for the microparticles to agglomerate during drying to make their final use easier, such as faster dissolution in the associated liquid. However, existing nebulizers are not suitable for easy modification to accommodate such changes in processing requirements.

[0009] Additionally, spray dryers tend to produce very fine particles, which can remain suspended in the drying gas exiting the drying system and must be filtered from the gas exiting the system. There is a need. Such fine particulate matter quickly clogs the filters, preventing efficient operation of the dryer and requiring frequent cleaning of the filters. Existing spray dryers also commonly utilize complex cyclone separation and filtering mechanisms to remove suspended particulate matter. Such equipment is expensive and requires costly maintenance and cleaning.

[0010] Another problem with spray drying systems is that the finished product can be compromised after the drying process is completed. In particular, exposure to wet process gases, excessive heat, or oxygen can compromise the finished product. For example, some spray-dried products are very hygroscopic and can reabsorb moisture after the spray-drying process is complete if the product is exposed to a wet dryer exhaust stream for an extended period of time. . Although evaporative cooling protects the spray-dried product from being damaged by its exposure to heat during the spray-drying process, some spray-dried products are exposed to high temperatures only for short periods of time before they begin to deteriorate or otherwise deteriorate. can't stand. Thus, prolonged exposure to the heated exhaust stream can damage the product. Additionally, some products may oxidize when exposed to oxygen after the drying process is complete.

[0011] Another problem with spray drying systems is that the finished product can be compromised after the drying process is completed. In particular, exposure to wet process gases, excessive heat, or oxygen can compromise the finished product. For example, some spray-dried products are very hygroscopic and can reabsorb moisture after the spray-drying process is complete if the product is exposed to a wet dryer exhaust stream for an extended period of time. . Although evaporative cooling protects the spray-dried product from being damaged by its exposure to heat during the spray-drying process, some spray-dried products are exposed to high temperatures only for short periods of time before they begin to deteriorate or otherwise deteriorate. can't stand. Thus, prolonged exposure to the heated exhaust stream can damage the product. Additionally, some products may oxidize when exposed to oxygen after the drying process is complete.

[0012] It is an object of the present invention to provide a spray drying system adapted for more efficient and versatile operation.

[0013] Another object is to provide an electrostatic spray drying system as characterized above that is relatively small in size and reliable in operation.

[0014] Yet another object is to provide an electrostatic spray drying system that can be installed and operated in locations that are relatively low in height and do not require special buildings or ceilings.

[0015] A further object is to provide an electrostatic spray drying system of the type described above that is effective for spray drying different product lots without cross-contamination.

[0016] Yet another object is to provide an electrostatic spray drying system of the above kind that is readily modifiable in both size and processing technique for specific drying applications.

[0017] A further object is to provide an electrostatic spray drying system operable to dry powders so as to agglomerate the particulates into a form that is easier for subsequent use.

[0018] Yet another object is to provide an electrostatic spray drying system that can be operated effectively, and thus more economically, with less heating requirements. A related object is to provide a spray drying system of the type operable to effectively dry temperature sensitive compounds.

[0019] Another object is a modular electrostatic spray dryer that can be selectively utilized for different capacity drying requirements and facilitates repair, maintenance, and module replacement without shutting down the spray drying system. It is to provide a system.

[0020] Yet another object is to provide an electrostatic spray drying system of the above type that is less susceptible to electrical malfunctions and dangerous explosions from fine powders and heated atmospheres within the drying chamber of the system. . A related object is to provide effective control of a spray drying system to monitor and control possible electrical malfunctions of the system.

[0021] Another object is a type of spray drying system having a filter system for more effective and efficient removal of suspended particulate matter from the drying gas exiting the dryer, with less maintenance requirements. is to provide

[0022] A further object is to provide a spray drying system as characterized above, wherein the dry gas filter system comprises means for automatically and more effectively removing particulate matter buildup on the filter. It is to be.

[0023] Yet another object is to provide an electrostatic spray drying system that is relatively simple in construction and lends itself to economical manufacture.

[0024] Another object is to provide a spray drying system that protects the finished product from damage.

[0025] Other objects and advantages of the present invention should become apparent upon reading the following detailed description and upon reference to the drawings.

1 is a side view of a powder processing tower of an exemplary spray drying system; FIG. 2 is a vertical sectional view of the powder processing tower shown in FIG. 1; FIG. 1 is an exploded perspective view of an exemplary powder processing tower; FIG. 1 is a plan view of an unassembled flexible impermeable liner usable in an exemplary powder processing tower; FIG. Figure A1 is a plan view of an alternative embodiment of a liner similar to that shown in Figure A1 but made of a permeable filter material; FIG. 4 is a plan view of another alternative embodiment of a liner, in this case made partly from impermeable material and partly from permeable filter material, usable in the illustrated powder processing tower; . FIG. 4 is a plan view of another alternative embodiment of a liner, in this case made of an impermeable, non-conductive rigid material, usable in the illustrated powder processing tower; 1 is an enlarged top view of the top cap or lid of an exemplary powder processing tower with a centrally supported electrostatic spray nozzle; FIG. 5 is a side view of the top cap and spray nozzle assembly shown in FIG. 4; FIG. 1 is an enlarged vertical cross-sectional view of an exemplary electrostatic spray nozzle assembly; FIG. FIG. 4 is an enlarged partial cross-sectional view of a nozzle support head of an exemplary electrostatic spray nozzle assembly; FIG. 4 is an enlarged partial cross-sectional view of the discharge end of an exemplary electrostatic spray nozzle assembly; 9 is a partial cross-sectional view similar to FIG. 8 showing a spray nozzle assembly having a modified ejecting spray tip to facilitate atomization of more viscous liquids; FIG. 9 is a cross-sectional view of an exemplary electrostatic spray nozzle assembly taken on line 9-9 of FIG. 8; FIG. FIG. 4 is an enlarged partial cross-sectional view of the powder collection cone and filter element housing of the exemplary powder processing tower; 11 is an exploded perspective view of the powder collection cone and filter element housing shown in FIG. 10; FIG. FIG. 4 is a partial cross-sectional side view of an alternative embodiment of a filter element housing for use with the illustrated powder processing tower; 12 is an enlarged partial cross-sectional view of one of the filters of the filter housing shown in FIG. 11, showing the reverse flow gas pulse filter cleaning device in an inoperative state; FIG. 11B is an enlarged partial cross-sectional view similar to FIG. 11A showing the reverse flow gas pulse air filter cleaning device in operation; FIG. FIG. 10 is a side view of an alternate embodiment of the filter element housing and powder collection chamber; 13 is a plan view of the filter element housing and powder collection chamber shown in FIG. 12; FIG. 13 is an enlarged partial cut-away view of the filter element housing and powder collection chamber shown in FIG. 12; FIG. 13 is an exploded perspective view of the filter element housing and associated upstream air directing plenum shown in FIG. 12; FIG. FIG. 5 is a partial cross-sectional view showing a fastening mechanism for securing the top cover to the drying chamber with an associated top liner isolation ring assembly; FIG. 13 is a partial cross-sectional view similar to FIG. 12 but showing a fastening mechanism for securing the drying chamber to the powder collection cone with the associated bottom liner isolation ring assembly; FIG. 4 is an enlarged partial view of one of the illustrated fasteners; 1 is a schematic diagram of an exemplary spray drying system; FIG. FIG. 4 is a schematic diagram of an alternative embodiment of a spray dryer operable to spray cool a melt stream into solidified particles; FIG. 4 is a partial cross-sectional view showing a fluid feed pump and associated drive motor for an exemplary spray drying system; FIG. 4 is a vertical cross-sectional view of an exemplary fluid supply pump supported within an outer non-conductive housing; FIG. 4 is an enlarged top view of an exemplary insulating liner and its isolation ring support assembly; FIG. 18 is an enlarged top view similar to FIG. 17 but showing an isolation ring assembly supporting a smaller diameter insulating liner; FIG. 4 is an enlarged side view of the top cap of an exemplary powder processing tower supporting multiple electrostatic spray nozzle assemblies; 20 is a top view of the top cap shown in FIG. 19; FIG. Vertical of an exemplary powder processing tower modified to support an electrostatic spray nozzle centrally adjacent to the bottom of the drying chamber of the powder processing tower, upwards of the liquid to be atomized for drying. It is a sectional view. 22 is a schematic side view of the bottom mounting support of the electrostatic spray nozzle assembly shown in FIG. 21; FIG. 23 is a top view of the electrostatic spray nozzle assembly and bottom mounting support shown in FIG. 22; FIG. Figure 24 is an enlarged cross-sectional view of one of the support rods for the spray nozzle bottom mounting support shown in Figures 22 and 23; 4 is a table showing alternative configurations for an exemplary powder drying system; FIG. 4 is a schematic diagram of an alternative embodiment of a spray drying system in which unused nitrogen gas is introduced into the gas recycle line of the system; FIG. 4 is a schematic diagram of another alternative embodiment of a spray drying system utilizing a cyclone separator/filter bag assembly to filter particulate matter from a recirculating dry gas stream. Similar to FIG. 25B, an alternative embodiment in which the dried particulates separated in the cyclone separator are reintroduced into the drying chamber. Fig. 10 is another alternative embodiment of a spray drying system having multiple fluidized bed filters for filtering particulate matter from recirculating drying gas; 1 is a flow diagram of a method of operating a voltage generator fault recovery method for use with an electrostatic spray drying system according to the present disclosure; 1 is a flow diagram of a method of modulating the pulse width of an electrostatic spray nozzle for use in an electrostatic spray drying system according to the present disclosure; 1 is a schematic top view of a modular spray drying system with multiple powder treatment towers; FIG. 29 is a front view of the modular spray drying system shown in FIG. 28; FIG. FIG. 29 is a top view of a modular spray drying system similar to FIG. 28 but with an additional powder treatment tower; FIG. 4 is a side view of an alternative embodiment of a powder collection system; 32 is an enlarged cross-sectional view of the collection container of the powder collection system of FIG. 31; FIG. Figure 33 is a schematic diagram of a blanket gas supply system for the powder collection system of Figures 31 and 32; FIG. 4 is a schematic diagram of an alternative embodiment of a spray dryer operable to spray cool a melt stream into solid particles; 35 is an enlarged cross-sectional view of a pulsed spray nozzle assembly of the spray drying system of FIG. 34; FIG.

[0079] While the invention is susceptible to various modifications and alternative constructions, specific exemplary embodiments thereof have been shown in the drawings and are described in detail below. However, there is no intention to limit the invention to the particular forms disclosed, but on the contrary the invention covers all modifications, alternative constructions and equivalents included within the spirit and scope of the invention. It should be understood that it is intended that

[0080] Referring now to the drawings in more detail, there is shown an exemplary spray drying system 10 according to the present invention, comprising a drying chamber 12 in the form of an upright cylindrical structure, a heated air A top closure mechanism in the form of a cover or lid 14 for the drying chamber 12 having an inlet 15 and a liquid spray nozzle assembly 16, and a bottom closure mechanism in the form of a powder collection cone 18 supported at the bottom of the drying chamber 12. It comprises a treatment tower 11 , a filter element housing 19 with a powder collection cone 18 extending therethrough and having a heated air outlet 20 , and a bottom powder collection chamber 21 . Drying chamber 12, collection cone 18, filter element housing 19, and powder collection chamber 21 are all preferably made of stainless steel. Top cover 14 is preferably made of plastic or other non-conductive material and in this case supports spray nozzle assembly 16 centrally. The illustrated heated air inlet 15 is oriented to direct heated air into the drying chamber 12 in a tangentially swirling direction. Frame 24 supports treatment tower 11 in an upright state.

[0081] According to an important aspect of the present embodiment, as best shown in Figures 6-9, the spray nozzle assembly 16 quickly and efficiently dries the liquid slurry to a desired powder form. A pressurized air-assisted electrostatic spray nozzle assembly for directing a spray of charged particles into the drying chamber 12 for the purpose of drying. The illustrated spray nozzle assembly 16 can be of the type disclosed in International Application US2014/056728, comprising a nozzle support head 31, an elongated nozzle barrel or body 32 extending downstream from the head 31, and an elongated nozzle body 32. and a discharge spray tip assembly 34 at the downstream end of the. The head 31 in this case is made of plastic or other non-conductive material and includes a radial liquid inlet which receives and communicates with a liquid inlet fitting 38 for coupling to a supply line 131 which communicates with the liquid supply. A passageway 36 is formed. The liquid supplied can include a solvent such as water, desired ingredients such as flavorings, food products, pharmaceuticals, etc., and liquid slurries containing carriers, as known in the art to dry to a desired powder form. It will be appreciated that any of a variety of slurries or similar liquids that can be dried into powder form such that the ingredients are encapsulated within the carrier. Other forms of slurries can also be used, including liquids that do not contain a carrier or that do not require encapsulation of the dried product.

[0082] The nozzle support head 31 in this case includes, downstream of said liquid inlet passage 36, a radial pressurization chamber which receives and communicates with an air inlet fitting 40 coupled to a suitable pressurized gas supply. An air atomization inlet passage 39 is further formed. The head 31 also has an end portion 44a extending into the passageway 41 in electrical contact with an electrode 48 axially supported within the head 31 and extending downstream of the liquid inlet passageway 36. It has a radial passageway 41 upstream of the liquid inlet passageway 36 for receiving a fitting 42 for securing a connected high voltage cable 44 .

[0083] To allow liquid to pass through the head 31, the electrode 48 is formed with an internal axial passage 49 that communicates with the liquid inlet passage 36 and extends downstream through the electrode 48. As shown in FIG. Electrode 48 is formed with a plurality of radial passages 50 communicating between liquid inlet passage 36 and internal axial passage 49 . The illustrated electrode 48 has a downstream outwardly extending radial hub 51 that fits within the counterbore of the head 31 with a sealing O-ring 52 interposed therebetween.

[0084] Elongated body 32 is in the form of an outer cylindrical member 55 made of plastic or other suitable non-conductive material, with upstream end 55a extending into the threaded bore of head 31. A sealing O-ring 56 is interposed between the cylindrical member 55 and the head 31 in threadable engagement. A liquid supply tube 58 made of stainless steel or other conductive metal is used to define a liquid flow path 59 for liquid communication between the axial electrode liquid passage 49 and the ejector spray tip assembly 34, and It extends axially through the outer cylindrical member 55 to define an annular atomizing air passageway 60 between the liquid supply tube 58 and the outer cylindrical member 55 . The upstream end of the liquid supply tube 58 projecting above the threaded inlet end 55 a of the outer cylindrical nozzle body 55 is electrically conductive within the cylindrical bore 65 opening below the electrode hub 51 . Mate. It can be seen that as the electrode 48 is charged by the high voltage cable 44 , the liquid supply to the inlet passage 36 is charged while passing through the electrode passage 49 and the liquid supply tube 58 along the entire length of the elongated nozzle body 32 . . The pressurized gas in this case passes through the radial air inlet passage 39 around the upstream end of the liquid supply tube 58 and then into the annular air passage 60 between the liquid supply tube 58 and the outer cylindrical member 55. communicate.

[0085] The liquid supply tube 58 is placed in electrical contact with the electrode 48 to effectively charge the liquid throughout its passage from the head 31 through the elongated nozzle body member 32 to the ejected spray tip assembly 34. placed. To that end, the dispensing spray tip assembly 34 includes a spray tip 70 having an upstream cylindrical section 71 surrounding the downstream end of the liquid supply tube 58 with a sealing O-ring 72 interposed therebetween. The spray tip 70 comprises an inwardly tapering or conical intermediate section 74 and a downstream cylindrical nose section 76 that defines a cylindrical flow path 75 and a liquid discharge orifice 78 of the spray tip 70 . The spray tip 70 in this case has a segmented radial retaining flange 78 extending outwardly of the upstream cylindrical section 71 defining a plurality of air passages 77 as will be apparent.

[0086] To direct the liquid from the supply tube 58 to the spray tip 70 while keeping the liquid charged as it is directed through the spray tip 70, a conductive pin unit 80 is attached to the downstream end of the supply tube 58. is supported within the spray tip 70 in electrical contact therewith. The pin unit 80 in this case comprises an upstream cylindrical hub section 81 formed with a downstream conical wall section 82 supported within the intermediate conical section 74 of the spray tip 70 . Cylindrical hub section 81 is formed with a plurality of circumferentially spaced radial liquid passages 83 (FIG. 8) communicating between liquid supply tube 58 and cylindrical spray tip passage section 75 . It can be seen that the conductive pin unit 80 , when seated within the spray tip 70 , provides physical support against the downstream end of the liquid supply tube 58 against which it abuts.

[0087] To concentrate charge on the liquid ejected from the spray tip, the pin unit 80 is concentric with the spray tip passageway 75 such that the liquid ejection orifices 78 are arranged annularly around the electrode pin 84. has a downwardly extending central electrode pin 84 supported on the . The electrode pin 84 has a tapered pointed end that extends beyond the annular spray tip discharge orifice 78 a distance such as about 1/4 to 1/2 inch. As the liquid exits the spray tip 70, the increased liquid contact around the protruding electrode pins 84 further increases the concentration of charge on the ejected liquid for enhancing liquid particle breakdown and distribution.

[0088] Alternatively, as shown in FIG. 8A, for spraying a more viscous liquid, the dispensing spray tip assembly 34 has a hub section 81 similar to that above but without the downwardly extending central electrode pin 84. can have This configuration allows more viscous liquids to pass more freely through the spray tip, and the charge ejecting the liquid further promotes liquid breakdown to dry such viscous liquids more efficiently. .

[0089] Dispensing spray tip assembly 34 further comprises an air or gas cap 90 positioned around spray tip 70 defining an annular atomizing air passageway 91 around spray tip 70. , spray tip 70, pin unit 80, and liquid supply tube 58 are assembled together and held electrically conductive. The air cap 90 of this example defines a conical pressurized air channel section 91 a around the downstream end of the spray tip 70 , which extends into the spray tip retaining flange 78 . Circumferentially spaced air passages 77 communicate with the annular air passage 60 between the liquid supply tube 58 and the outer cylindrical member 55 for pressure through an annular discharge orifice 93 about the spray tip nose 76 . It directs the compressed air or gas discharge stream and liquid exiting the spray tip liquid discharge orifice 78 . The air cap 90 has an upstream cylindrical end 95 that threads around the downstream male threaded end of the outer cylindrical member 55 to hold the internal components of the spray nozzle assembled. Air cap 90 defines a segmented radius of spray tip 70 to support spray tip 70 and, in turn, conductively support pin unit 80 and liquid supply tube 58 to upstream electrode 48 . It has a counterbore 96 that receives and supports the directional flange 78 .

[0090] The spray nozzle assembly 16 is operable to eject a spray of charged liquid particles into the drying chamber 12. As shown in FIG. In practice, it has been found that the illustrated electrostatic spray nozzle assembly 16 can be operated to produce droplets of extremely fine liquid particles, such as on the order of 70 microns in diameter. As will be apparent, due to the breakdown and repulsive nature of such fine liquid spray particles and heated drying gas introduced into the drying chamber, liquid The particles undergo rapid and efficient drying into fine particle form. Although the illustrated electrostatic spray nozzle assembly 16 has found particular utility in connection with the present invention, it can be used with known types of hydraulic rotary electrostatic spray nozzles and high volume low pressure electrostatic spray nozzles. It will be appreciated that other electrostatic spray nozzles and systems can also be used, including.

[0091] According to a further important feature of this embodiment, the drying chamber 12 is concentrically spaced apart from the inner wall surface 12a of the drying chamber 12 from which the charged liquid spray particles from the spray nozzle assembly 16 are expelled. It has an internal non-metallic insulating liner 100 that is sealed. As shown in FIG. 2, the liner preferably has a diameter less than the inner diameter d1 of the drying chamber 12 to provide an insulating air gap 101 of at least 2 inches (about 5 cm) to the outer wall surface 12a of the drying chamber 12. d, but other dimensions can be used. In this embodiment, the liner 100 is non-structural, preferably made of an impermeable flexible plastic material 100a (FIGS. 3 and 3A). Alternatively, as will become apparent, the liner 100 can be made of a rigid impermeable non-conductive material 100c (FIG. 3D), a permeable filter material 100b (FIG. 3B), or a partially impermeable material 100a and partially transmissive. 100b (FIG. 3C).

[0092] According to another aspect of the present embodiment, the treatment tower 11 has a quick disconnect assembly configuration that facilitates the assembly and installation of the annular liner 100 so as to be electrically insulated against the outer wall of the drying chamber 12. have As such, the annular insulating liner 100 is supported at both ends by respective upper and lower isolation ring assemblies 104 (FIGS. 1, 3, 13, 13A, 14, and 17). Each ring assembly 104 in this case comprises an inner cylindrical isolation ring 105 to which the end of the liner 100 is attached, and a plurality of radially fixed, circumferentially spaced non-conductive rings extending outwardly relative to the isolation ring 105 . and a stand-off stud 106 of flexible, polypropylene, or other plastic. In the illustrated embodiment, the top end of the liner 100 is folded over the top of the isolation ring 105 of the top ring assembly 104 and positioned over the folded ends of the liner 100 and isolation ring 105 (FIG. 13). It is attached to it by an annular U-shaped rubber gasket 108 . The lower end of liner 100 is similarly oriented around the bottom of isolation ring 105 of lower ring assembly 104 and secured thereto by a similar rubber gasket 108 (FIG. 13). Similar rubber gaskets 108 are also supported within the ends of cylindrical isolation ring 105 of ring assembly 104 to protect liner 100 from damage by the exposed edge of isolation ring 105 .

[0093] To secure each isolation ring assembly 104 within the drying chamber 12, a respective mounting ring 110 is attached to the outside of the drying chamber 12, such as by welding. A stainless steel mounting screw 111 extends through aligned holes in the mounting ring 110 and the outer wall of the drying chamber 12 to threadably engage the insulating isolation stud 106 . A rubber O-ring 112 in this example is provided around the end of each standoff stud 106 to seal against the inner wall of the drying chamber 12, and a neoprene connection sealing washer 114 is attached to the head of each retaining screw 111. placed around.

Circumferentially spaced locations intermediate the isolation studs 106 to secure the drying chamber top cover 14 in place on the drying chamber 12 to seal against the top isolation ring assembly 104 . , an annular array 120 (FIGS. 1 and 2) of spaced apart releasable latch assemblies 121 are secured to the mounting ring 110 (FIGS. 13-14). Latch assembly 121 is positionable over the upper peripheral edge of cover 14 to secure upper cover 14 to U-shaped gasket 108 around the upper edge of isolation ring 105 and around the upper edge of cylindrical drying chamber 12 . has an upwardly extending draw hook 122 which is drawn into a locked position upon downward pivotal movement of the latch arm 124 to the latched position to hold against a similarly large diameter annular U-shaped gasket 126 of the It can be of any known type. Latch assembly 121 can be easily unlatched by pivoting back latch hook 124 and moving draw hook 122 upward and outward to allow removal of top cover 14 if desired. . A similar annular array 120a of latch assemblies 121 is provided around the mounting ring 110 adjacent the bottom of the drying chamber 12, where the draw hooks 124 are raised relative to the outwardly extending flange 129 of the collection cone 18. and the flange 129 of the collection cone 18 to seal against the rubber gaskets 108, 126 at the bottom edge of the isolation ring 105 and the cylindrical bottom edge of the drying chamber 12 (Fig. 13A). It will be appreciated that in a particular application, the liner 100, O-rings and other sealing gaskets 108, 126 may or may not be made of FDA compliant materials.

[0095] During operation of the electrostatic spray nozzle assembly 16, liquid supplied to the electrostatic spray nozzle assembly 16 from a liquid supply, in this case a liquid holding tank 130 as shown in FIG. Assembly 16 leads into effective drying zone 127 defined by annular liner 100 . Liquid is connected from a liquid supply holding tank 130 to the liquid inlet fitting 38 of the spray nozzle assembly 16 via a pump 132, preferably a peristaltic dosing pump having a liquid diverting roller system operable in a conventional manner. supplied through a separate liquid supply or delivery line 131 . As shown in FIG. 16A, the peristaltic dosing pump 132 in this case comprises three electrically insulated pump rollers 33 of plastic within a plastic pump housing 37 . The liquid supply or delivery line 131 in this case is electrically shielded tubing and the stainless steel drying chamber 12 is preferably approved through a support frame 24 that secures it by metal-to-metal contact. grounded by a ground line.

[0096] An electronic controller 133 controls the various actuators and electrical components of the electrostatic spray drying system, such as the electric motor 134, the pump 132, the liquid spray nozzle assembly 16, the high voltage generator that provides voltage to the high voltage cable 44, and the like. or operatively connected to electronic devices and act to control their operation. Although a single controller is shown, it should be understood that a distributed controller configuration including multiple controllers may be used. As shown, controller 133 may operate according to a program, such as a programmable logic controller. For clarity, various operable connections between controller 133 and various other components of the system have been omitted from FIG.

[0097] According to a further aspect of the present embodiment, the pump 132, and the liquid connecting the pump 132 to the spray nozzle assembly 16, prevents charging of the motor 134 from the liquid charged by the spray nozzle assembly 16. It is operated by an electric motor 134 (FIG. 16) arranged in electrical isolation with respect to the supply line 131 . As such, the drive motor 134 has an output shaft 135 connected to a pump head drive shaft 136 by a non-conductive drive segment 138 made of rigid nylon or the like that insulates the pump 132 from the electric drive motor 134 . The non-conductive drive segment 138 in the illustrated embodiment has a diameter of approximately 1.5 inches (approximately 3.8 cm) and an axial length of approximately 5 inches (approximately 12.7 cm). The electric motor drive shaft 135 supports a mounting plate 139 which in this case is secured to a non-conductive drive segment 138 by screws 141 . Pump head drive shaft 136 similarly supports a mounting plate 140 secured by screws 141 to the opposite end of non-conductive drive segment 138 .

[0098] An electrostatic voltage generator 222 is electrically connected to the nozzle assembly 16 via an electrical line 224 to provide a voltage that charges the atomized liquid droplets. In the illustrated embodiment, electrical line 224 is optional and includes a variable resistor element 226 that can be manually or automatically adjusted to control the voltage and current applied to spray nozzle assembly 16 . An optional ground wire 228 is also electrically connected between the liquid supply line 131 and ground 232 . Ground line 228 includes a variable resistor 230 that can be manually or automatically adjusted to control the voltage present in the fluid. In the illustrated embodiment, a ground wire is placed in front of pump 132 to control the charge state of the fluid provided to the system. The system can further include a sensor that communicates the charge state of the fluid to the controller 133 so that the system controls the resistance of the variable ground resistor 230 and bleeds off charge from the liquid lines in the system to The charge state of the liquid can be automatically monitored and selectively controlled.

[0099] The drive motor 134 of this example is also well grounded and supported within a non-conductive plastic motor mounting housing 144 . The illustrated liquid holding tank 130 is supported on a liquid level gauge 145 that allows monitoring of the amount of liquid in the tank 130 , and an electrically insulating barrier 146 is between the bottom surface of the liquid holding tank 130 and the liquid level gauge 145 . provided to Instead of peristaltic pump 132, plastic pressure pots can be used, as well as other types of pumps and fluid delivery systems that can be electrically isolated from their electrical operating system.

[0100] The pressurized gas, which is directed to the atomizing air inlet fitting 18 of the spray nozzle assembly 16, in this case passes to and from the atomizing air inlet fitting 18 of the spray nozzle assembly 16 via gas supply line 151 (Fig. 15). It originates from a communicating bulk nitrogen supply 150 . A gas heater 152 is provided in supply line 151 to enable dry inert nitrogen gas to be supplied to spray nozzle assembly 16 at a controlled temperature and pressure. Although nitrogen is described as the atomizing gas in the context of this embodiment, the oxygen level in the drying chamber may cause a spark or other electrical discharge from the electrostatic spray nozzle assembly or other electronically controlled element of the drying system. Other inert gases can be used, or other gases can be used with air, as long as they are maintained below a level that creates a combustion atmosphere with dry powder particles in the drying chamber that can ignite due to mechanical failure. be understood.

[0101] According to a further important aspect of this embodiment, a heated nitrogen mist is supplied to the spray nozzle assembly 16 and directed into the drying chamber 12 when atomization of the liquid sprayed into the drying chamber 12 occurs. The drying gas is continuously recirculated through the drying chamber 12 as a drying medium. 15, the drying gas introduced into the drying chamber 12 from both the drying gas inlet 15 and the spray nozzle assembly 16 circulates through the length of the drying chamber 12 and into the drying chamber 12. Efficient drying of atomized charged liquid particles into powder form. The dry powder travels through powder collection cone 18 into powder collection chamber 21 where it can be removed by suitable means, manually or by other automated means.

[0102] As best shown in FIGS. 10 and 10A, the illustrated powder collection cone 18 includes an upper cylindrical section 155, an inwardly tapering conical middle section 156, and a dry powder collecting cone 156. and a lower cylindrical powder delivery section 158 extending centrally through the filter element housing 19 to lead into the body collection chamber 21 . The filter element housing 19 has in this case a pair of vertically stacked annular HEPA filters 160 spaced and outwardly mounted to the lower section of the powder collection cone 18 . The illustrated powder collection cone 18 has an outwardly extending radial flange 161 intermediate its end located above an upper filter 160 within the filter element housing 19, and an annular seal 162 provides a radial Interposed between flange 161 and filter element housing 19 . While most of the dry powder falls down through the powder collection cone 18 into the powder collection chamber 19 , the fine particles move upward around the bottom section of the powder collection cone 18 and then into the filter housing 19 . Only the finest particles are carried into the drying gas as they travel outward through the HEPA filter 160 which suppresses and filters out fines before exiting through the exhaust gas outlet 20 of the remain.

[0103] Alternatively, as shown in Figures 11, 11A, and 11B, a plurality of circumferentially spaced cylindrical filters 160a mounted to depend vertically from an intermediate transverse support panel 163 of the housing 19a. A filter element housing 19a can be used that includes a. Gas laden with powder particles directed from the collection cone 18 into the lower collection chamber passes through the filter 160a and into a common exhaust plenum 164 within the filter element housing 19a on the transverse support panel 163 through the filter 160a. It flows transversely and communicates through outlet port 20a with particles that are restricted from the airflow by filter 160a. To periodically clean the filters 160a, each filter 160a may be cleaned according to commonly assigned U.S. Pat. No. 8,876,928, the disclosure of which is incorporated herein by reference. It has a respective countercurrent pulse air filter cleaning device 167 of the disclosed type. Each of the backflow pulse air filter washers 167 has a respective gas supply line 167a for connection to a pulsed air supply.

[0104] The exemplary countercurrent pulse air filter cleaning devices 21, as shown in Figures 11A and 11B, each have an annular air filter for connection to a compressed gas supply line 167a that is connected to a pressurized gas source, such as nitrogen. It includes a reverse flow pulse nozzle 240 having a gas inlet 241 in the top wall of exhaust plenum 164 secured by retainer 242 . Nozzle 240 has a cylindrical closed bottom configuration that defines a hollow internal air passageway 244 extending from inlet 241 through exhaust plenum 164 and substantially the length of filter 160a. The nozzle 240 is formed with a plurality of relatively large diameter discharge holes 246 in a section within the exhaust plenum 164 and a plurality of smaller sized air discharge holes 248 along the length of the nozzle 240 within the filter 160a. be.

[0105] During operation of the reverse flow pulse nozzle 240, axial movement within the exhaust plenum 164 between the exhaust port open and closed positions to block the flow of process gas from the filter element housing 19a to the exhaust plenum 164. For this purpose, an annular exhaust port blocking plunger 249 is positioned above the reverse flow pulse nozzle 160a. A bottom-opening plunger cylinder 250 is mounted to depend and seal from the top wall of the discharge plenum 164 to control movement of the plunger 249 . The illustrated plunger 249 includes an upper relatively small diameter annular sealing and diverting flange 252 having an outer circumference configured for sliding sealing engagement with the interior of the cylinder 250 and an exhaust port in the panel 163 . and a lower larger diameter valve head 254 positioned below the lower distal end of cylinder 250 in sealing engagement with 253 . Plunger 249 is preferably made of a resilient material and upper sealing and diversion flange 252 and lower valve head 254 have a downwardly tapering or cup-shaped configuration.

[0106] The plunger 249 is positioned such that axial movement along the counterflow pulse nozzle 240 is restricted, and is secured by a coil spring 256 around the circumference of the counterflow pulse nozzle 240 to provide a force as shown in FIG. , is biased to its normal open or retracted position. With valve plunger 249 biased to this position, process gas flows from filter element housing 19a, through filter 160a, exhaust port 253, and into exhaust plenum 164. FIG.

[0107] During a backflow pulse gas cleaning cycle, a pulse of compressed gas is directed through backflow pulse nozzle 240 from inlet line 167a. As the compressed gas travels through the nozzle 160a, it is first directed through the large diameter or plunger actuation hole 246 into the plunger cylinder 250 above the plunger seal and diverting flange 252 and then the smaller diameter. It is led through the reverse flow pulse nozzle hole 248 . The larger holes 249 provide a path of less resistance so that the gas initially enters the plunger cylinder 250 and as the pressure within the plunger cylinder 250 increases, pushes the plunger 249 against the biasing force of the spring 256. push downwards. Eventually, the pressure increases to the point that it overcomes the force of spring 256 and forces plunger 249 downward toward exhaust port 253 , temporarily sealing exhaust port 253 . After the plunger 249 seals the exhaust port 253, the compressed gas in the outer plunger cylinder 250 can no longer move the plunger 249 and the gas pressure in the plunger cylinder 250 increases to a point and then Compressed gas is forced through smaller nozzle holes 248 against filter 160a to dislodge particulate matter buildup around its perimeter.

[0108] Following the backflow compressed air pulse and removal of particles that have accumulated on filter 160a, the pressure is reduced within plunger cylinder 250 to the extent that it no longer opposes spring 256. FIG. Plunger 249 then moves upward to its retracted or rest position under the force of spring 256 to unseal discharge port 253 for continued operation of the dryer.

[0109] Yet another alternative embodiment of an exhaust gas filter element housing 270 and a powder collection chamber 271 mountable on the lower end of the drying chamber 12 is shown in FIGS. 12-12B. In this case, an upper powder diversion plenum 272 is attachable to the underside of the elongated drying chamber 12, the filter element housing 270 includes a plurality of vertically oriented cylindrical filters 274, and a powder diversion plenum 270 is included. Located below the plenum 272 , a powder diverting cone 275 is connected to the lower surface of the filter element housing 270 and the powder collection chamber 271 is supported on the lower surface of the powder diverting cone 275 .

[0110] The illustrated powder directing plenum 272 is sealingly mountable against the lower surface of the drying chamber 12 and has an opening for receiving the drying gas and powder from the drying chamber 12 and the drying zone 127. It includes an outer cylindrical housing wall 289 having an upper end. Contained within the powder directing plenum 272 forms a discharge chamber 282 (FIG. 12B) on its lower surface and on its upper side directs the drying gas and powder from the drying chamber 12 to the outer periphery of the conical discharge plenum 281 . There is a downwardly opening conically configured exhaust plenum 281 that leads downwardly and outwardly around the .

[0111] The filter element housing 270 has an outer cylindrical housing wall 284 sealingly attached to the bottom periphery of the powder directing plenum 272 by an annular seal 285 and an annular seal 288 to form a conical exhaust. and an inner cylindrical filter shroud 286 sealingly attached to the bottom periphery of the plenum 281 . Conical exhaust plenum 281 and inner cylindrical filter shroud 286 are supported within outer cylindrical housing wall 289 of gas directing plenum 272 and filter element housing 270 by a plurality of radial supports 290 (FIG. 12A) to provide a conical shape. A powder directing plenum 272 is provided to form an air passageway 291 communicating around the bottom periphery of the discharge plenum 281 and an annular gas passageway 292 between the inner cylindrical filter shroud 286 and the outer cylindrical housing wall 284 . Gases and powder passing therethrough are directed outwardly around the filter element shroud 281 by the conical discharge plenum 281 into the underlying powder diverting cone 275 and collection chamber 271 .

[0112] Cylindrical filter 274 is supported in this case to depend against a circular support plate 295 which is fixedly positioned below the lower surface of downwardly opening conical discharge plenum 281 . A circular filter support plate 295 is in this case mounted so as to be slightly recessed against the upper perimeter of the cylindrical shroud 286 and forms the bottom wall of the discharge chamber 282 . The illustrated cylindrical filters 274 each include a cylindrical filter element 296, a top cylindrical cartridge retaining plate 298, a bottom end cap with interposed annular sealing elements 300, 301, 302 and a sealing plate 299. It is in the form of a cartridge. To secure the filter cartridges in assembled relationship, the top cartridge retaining plate 298 passes through a central hole in the bottom end cap 299 which is secured by a nut 306 with an O-ring sealing ring 308 interposed therebetween. It has a depending U-shaped support member 304 with a threaded lower end stud 305 positionable on the bottom. The upper retaining plate 298 of each filter cartridge is sealingly mounted around a respective circular opening 310 in the central support plate 295 , with the filter elements 296 depending against the lower surface of the support plate 295 . Disposed, a central opening 311 in holder plate 298 provides communication between exhaust chamber 282 and the interior of cylindrical filter element 296 . The filter element cartridges are in this case circumferentially spaced around the center of the inner shroud 274 .

[0113] The filter element housing 270 in this example is secured to the powder directing plenum 272 by releasable clamps 315 or similar fasteners to allow easy access to the filter cartridge. An inner filter shroud 286 is also releasably attached to the cylindrical filter 274, such as by a pin and slot connection, to allow access to the filter for replacement.

[0114] During operation of the drying system, the drying gas and powder directed into the powder directing plenum 272 is routed around the conical discharge plenum 281 into the annular passages 291, 292 and around the inner filter element shroud 274. It will be seen that the powder flows downward into the powder direction cone 275 and into the collection chamber 271 where it is collected. As previously indicated, most of the dry powder remaining in the gas stream moves into the powder collection chamber 271, but as can be seen, the dry gas passes through the filter through the dry gas discharge plenum 282. Particulate matter carried by the fine gas is separated and retained by the annular filter 274 as it travels in, exits through the dry gas discharge port 320 and is recirculated to the drying chamber 12 .

[0115] Each of the cylindrical filters 274 has a respective backflow gas pulse washer 322 to clean powder build-up from the cylindrical filters 274 in the course of use of the drying system. As such, the gas directing plenum 272 has in this case an outer annular pressurized gas manifold channel 321 connected to a suitable pressurized air supply. Each backflow air pulse scrubber 322 has a respective pressurized gas connected between an annular pressurized gas manifold channel 321 and a respective control valve 326, in this case attached to the outer surface of the air directing plenum 272. It has a supply line 325 . A gas pulse diversion line or tube 328 extends radially from the control valve 326 through the conical walls of the air diversion plenum 272 and the exhaust plenum 329 and then to the terminating discharge end of the upwardly disposed gas pulse diversion line 328 . It makes a right angle turn downward at 329 and is aligned with the central opening 311 of the filter cartridge retaining plate 298 and the underlying cylindrical filter element 296 .

[0116] By suitable selective or automated control of control valve 326, control valve 26 discharges pulses of compressed gas from line 328 axially into circulation filter 274 and into the outer wall of cylindrical filter element 296. It can be operated periodically to remove accumulated powder on it. Preferably, the discharge end 329 of the pulse gas directing line 328 is spaced relative to the upper end of the circulation filter 274 to facilitate the directing of the compressed gas impulse to the filter element 296 while simultaneously exhausting it. Gas is drawn from chamber 282 , thereby facilitating a reverse flow impulse that removes accumulated powder from filter element 296 . Preferably, the discharge end 329 of the air tube 328 is spaced a distance from the top end of the cylindrical filter element so that upon reaching the filter cartridge, the expanding airflow, shown as 330 in FIG. It has a perimeter substantially corresponding to the diameter of central opening 311 in plate 298 . In the exemplary embodiment, air directing tube 28 has a diameter of approximately 1 inch and discharge end 329 is spaced from retaining plate 298 a distance of approximately 2.5 inches.

[0117] The powder collection chamber 271, in this case, is in a vertical or open position that allows the dry powder to be directed into the collection chamber 271 and the dry powder to the collection chamber 271 when the powder is removed. A circular butterfly valve 340 (powder collection chamber 271 (shown in FIG. 12B) in an isolated manner. Alternatively, it will be appreciated that the powder collection chamber 271 may deposit powder directly from the open bottom end onto the movable conveyor.

[0118] To enable recirculation and reuse of the dry gas exiting the filter element housing 19a, the exhaust outlet 20 of the filter housing 19 is connected to a recirculation line 165, which in turn: It is connected to the heating gas inlet port 15 of the top cover 14 of the heating chamber 12 through a condenser 166, a blower 168, and a dry gas heater 169 (FIG. 15). Condenser 170 removes any water vapor from the exhaust gas flow stream by means of chilled water cooling condenser coils 170a having respective chilled water supply and return lines 171,172. Condensate from the condenser 170 is directed to a collection vessel 174 or drain. The dry nitrogen gas is then directed by blower 168 through gas heater 169 which, after cooling in condenser 170, directs the dry gas to a predetermined heating temperature for the particular powder drying operation. Reheat and redirect back to heated gas inlet port 15 and into heating chamber 12 . A discharge control valve 175 connected to recirculation line 165 between blower 168 and heater 169 directs excess nitrogen gas introduced into the system from electrostatic spray nozzle assembly 16 to appropriate discharge line 176 . enable The exhaust flow from control valve 175 can be set to match the excess nitrogen gas introduced into drying chamber 12 by electrostatic spray nozzle assembly 16 . It is understood that selective control of exhaust flow control valve 175 and blower 168 can selectively control the vacuum or pressure level within drying chamber 12 for specific drying operations or to control evaporation and venting of volatiles. let's be In the illustrated embodiment, a cold water condenser 170 is shown, but it will be appreciated that other types of condensers or means for removing moisture from the recycle gas flow stream can be used.

[0119] The dry gas introduced into the effective drying zone 127 formed by the flexible liner 100 from both the electrostatic spray nozzle assembly 16 and the dry gas inlet port 15 is dried by the electrostatic spray nozzle assembly 16. It will be appreciated that a dry inert gas, ie nitrogen in the illustrated embodiment, facilitates drying of the liquid particles sprayed into the chamber 12 . Recirculation of the inert drying gas, as described above, also purges oxygen from the drying gas and, in the event of unintentional sparking from the electrostatic spray nozzle assembly 16 or other components of the system, removes powder from the drying chamber. Prevent potentially dangerous explosions.

[0120] Recirculation of the inert drying gas through the spray-drying system 10 also enables very energy-efficient operation of the spray-drying system 10 at significantly lower operating temperatures and correspondingly significantly lower costs. I know you can do it. As mentioned above, sprayed emulsions are generally made up of three components, for example water (solvent), starch (carrier) and flavor oil (core). In that case, the purpose of spray drying is to form starch around the oil and remove all water with the drying gas. The starch remains as a protective layer around the oil, preventing it from oxidizing. It has been found that this desired result is more easily achieved when the emulsion is negatively charged prior to and during atomization.

[0121] Although the theory of operation is not well understood, each of the three components of the atomized emulsion has different electrical properties. Water is the most conductive group and tends to attract the most electrons, followed by starches, and finally oils, which are the most resistive and attract few electrons. It is known that opposite charges attract and like charges repel, and water molecules that all have the most like charges are the most repulsive towards each other. This force directs the water molecules to the outer surface of the droplet, where they have the greatest surface area for the drying gas, thereby enhancing the drying process. Oil molecules with less charge remain in the center of the droplet. This process is believed to aid in faster drying or drying with a cooler heat source as well as a more uniform coating. In testing the spray-dried powder produced by the present spray-drying system operated at an inlet drying gas temperature of 90 degrees Celsius, the powder was dried in a conventional spray-drying process capable of operating at 190 degrees Celsius. I found it to be comparable. Moreover, in some instances, the present spray drying system can effectively operate without heating the drying gas.

[0122] The encapsulation efficiency, ie the uniformity of the dry powder coating, was also comparable to that achieved in the higher temperature spray drying. In addition, the lower temperature drying resulted in significantly less aromas, odors, and volatile components exhaled into the environment compared to conventional spray drying, and the outer surface of the dried particles was more uniformly and completely formed of starch. It was found to further show that Reducing the emission of fragrances and odors further enhances the work environment and eliminates the need to purge such odors that can be irritating and/or harmful to operating personnel. Low temperature processing also allows for spray drying of temperature sensitive ingredients without damage or adverse effects on the compound.

[0123] During the drying process, if any particles may stick to or otherwise accumulate on the surface of the liner 100, the liner 100 is periodically subjected to vibratory motion sufficient to remove any accumulated powder. A liner vibrator is provided to provide. In the illustrated embodiment, the drying chamber 12 has a side pneumatic liner oscillating valve port 180 connected to an air tank 181 that supplies pressurized air to the pneumatic liner oscillating valve port 180 . can be actuated periodically to lead it through the annular gap between the liner 100 and the outer wall of the drying chamber 12, vibrating the flexible liner 100 back and forth with sufficient force to remove any accumulated powder. get rid of Pressurized air is preferably directed to the pneumatic liner oscillating valve port 180 in a pulsed fashion to enhance such oscillating action. Alternatively, it will be appreciated that mechanical means can also be used to vibrate the liner 100 .

[0124] To ensure against cross-contamination between successive different selective uses of the spray-drying system, such as between different powder processes in the drying chamber 12, the quick-disconnect fastener 121 annular Arrays 120 , 120 a allow disassembly of cover 14 and collection cone 18 from drying chamber 12 for easy replacement of liner 100 . Because the liner 100 is made of relatively inexpensive materials, the liner 100 is disposable between different powder runs, allowing new, new replacement liners to be replaced without undue expense.

[0125] According to another important feature of this embodiment, the drying chamber 12 is easily modifiable for different spray drying requirements. For example, for smaller drying requirements, a smaller diameter liner 100a can be used to reduce the size of the effective drying zone. Thus, an isolation ring assembly 104a (FIG. 18) similar to that described above but having a smaller diameter inner isolation ring 105a can be readily replaced with a larger diameter isolation ring assembly 104. FIG. Replacing the ring assemblies unlatches the circumferentially spaced arrays 120, 120a of latches 121 with respect to the top cover 14 and collection cone 18, removes the larger diameter ring assemblies 104 from the drying chamber 12, and replaces them with This can be accomplished by replacing the smaller diameter ring assembly 104a and liner 100a, reassembling and relatching the top cover 14 and collection cone 18 onto the drying chamber 12. FIG. The smaller diameter liner 100a effectively reduces the drying zone into which the heated drying and atomizing gases are introduced, allowing faster and more energy efficient drying of smaller lots.

[0126] In further enabling more efficient drying of smaller lot processes, the drying chamber 12 has a modular configuration that allows for a reduction in the length of the drying chamber 12. In the illustrated embodiment, the drying chamber 12 includes a plurality, in this case two, vertically stacked cylindrical drying chamber modules or sections 185,186. Lower chamber section 186 has a shorter length than upper chamber section 185 . The two cylindrical drying chamber sections 185, 186 are again releasably secured to each other by an array 102b of circumferentially spaced quick disconnect fasteners 121 similar to those described above. The mounting ring 110 for this array 102b of fasteners 121 is welded to the upper cylindrical drying chamber section 185 adjacent its lower end, and the fasteners 121 of that array 102b are on the upper outer side of the lower cylindrical drying chamber section 186. It is oriented with the draw hook 122 positioned downwardly to engage and retain the underside of the radial flange 188 (FIGS. 1 and 2). During the release of the two arrays 102a, 102b of fasteners 121 attaching the lower cylindrical section 186 to the upper cylindrical section 185 and the collection cone 18, the lower cylindrical section 186 is removed and the lower isolation ring assembly 104 is replaced with the upper chamber section 185. , and liner 100 can be replaced with a shorter length liner. The fasteners 121 of the array 102b then powder the upper cylindrical drying chamber section 185 with the lower isolation ring assembly 104 therebetween and then the array 102b engages the outer annular flange 129 of the collection cone 18. Secure directly over the body collection cone 18 . This modification allows the use of a substantially shorter effective drying zone length, further reducing the heating requirements for drying smaller lots.

[0127] It will be appreciated that additional cylindrical drying chamber modules or sections 186 may be added to further increase the effective length of the drying chamber 12. FIG. As shown in FIGS. 19 and 20, multiple electrostatic spray nozzle assemblies 16 within the top cover 14, whether of increased size or not, to increase the amount of liquid sprayed into the drying chamber 12. can be provided. A plurality of spray nozzle assemblies 16, which may be fed from a common liquid and nitrogen supply, are preferably circumferentially aligned with each other within respective previously covered mounting holes 190 in the top cover 14 (FIG. 4). spaced apart. The unused central mounting hole 192 (FIG. 20) can then be appropriately covered or otherwise closed.

[0128] In accordance with yet another feature of the present embodiment, the modular quick disconnect components of the drying tower 11 further provide a position at the top of the drying chamber 12 for downward spray into the drying chamber 12. Allows repositioning of the electrostatic spray nozzle assembly 16 to a position adjacent the bottom of the drying chamber 12 for upward spraying of the charged liquid. To this end, the spray nozzle assembly 16 is removed from the top cover 14, in this case a bottom spray nozzle mounting support mounted within the upper cylindrical wall section 155 of the powder collection cone 18 immediately adjacent the bottom of the drying chamber 12. 195 (FIGS. 21-24) and directs the electrostatic spray nozzle assembly 16 to spray a charged spray pattern upward into the drying chamber 12 as shown in FIG. can. As shown in FIGS. 22-24, the illustrated bottom nozzle mounting support 195 includes a central annular mounting hub 196 for supporting the spray nozzle assembly 16 adjacent the upstream end, the central annular mounting. Hub 196 is supported within upper cylindrical section 155 of powder collection cone 18 by a plurality of radial mounting rods 198 made of non-conductive material. Each radial mounting rod 198 is cylindrically secured by a respective stainless steel screw 199 (FIG. 24) with a rubber connecting sealing washer 200 between the head of the screw 199 and the outer wall surface of the powder collection cone 18 . Secured to the profile wall section 155 , a sealing O-ring 201 is interposed between the outer end of each mounting rod 198 and the inner wall surface of the powder collection cone section 18 . Non-conductive Teflon or other plastic liquid and atomizing gas supply lines 205, 206, respectively, are connected radially outwardly to insulated fittings 208, 209, respectively, by powder collection cones 18 for powder collection. Cone 18 is connected to atomizing air and liquid supply lines 151 , 131 . A high voltage power cable 210 is also radially connected to the nozzle assembly through an insulated fitting 211 .

[0129] With the electrostatic spray nozzle assembly 16 mounted adjacent the lower surface of the drying chamber 12, the central spray nozzle mounting hole 192 in the cover 14 as well as the gas inlet port 15 can be suitably covered. The powder collection cone 18 further has a vertically oriented dry gas inlet 215 which can be uncovered and connected to a dry gas recirculation line 165, the cover 14 in this case being connected to a pair of outlets. It has a port 216 which is also uncovered for connection to the heated gas return line.

[0130] With the spray nozzle assembly 16 mounted on the underside of the drying chamber 12, charged liquid spray particles directed upward into the drying chamber 12 are dried by the drying gas, which in this case is The atomizing gas, which is also both a dry inert gas or nitrogen, is directed tangentially through the bottom heated gas inlet 215 by heating from the spray nozzle assembly 16 .

[0131] According to the present embodiment, as described above, the annular liner 100 within the drying chamber 12 preferably allows the drying gas to pass through the filter media and out of the top exhaust port 216 in the cover 14 to recirculate, Made of filter media 100b (FIG. 3B) to allow it to travel to recirculation line 165 for reheating and redirection to bottom gas inlet port 215. FIG. The powder dried by the upwardly directed drying and atomizing gases ultimately flows downwardly through the powder collection cone 18 into the collection chamber 19, as described above, where only the finest particles are retained. , are filtered by the filter media liner 100 . Additionally, the pneumatic liner vibrator can be operated periodically to prevent powder build-up on the liner 100 .

[0132] From the above, as shown in Table 220 of FIG. 25, the treatment tower can be readily configured and operated in various treatment modes for specific spray applications. The length of the drying chamber can be selectively varied by adding or removing cylindrical drying chamber sections 186, liner materials can be selectively determined such as impermeable or permeable, electrostatic The orientation of the spray nozzle can be varied between downward top spray or upward bottom spray, and the direction of the process gas flow can be varied between downward and upward based on the desired configuration.

[0133] In the above embodiments, nitrogen or other inert drying gas is introduced into the system as an atomizing gas to the electrostatic spray nozzle assembly 16; alternatively, nitrogen gas is introduced into the recirculating gas. can also In a spray drying system such as that shown in FIG. 25A, where parts similar to those described above are given similar reference numerals, as already mentioned, the nitrogen or other inert gas may It is introduced into gas heater 169 via line 169a, directed to drying chamber 100 via gas delivery and supply line 169a, and recycled from drying chamber 100 through condenser 170 and blower 168. In that embodiment, nitrogen gas can also be supplied to the electrostatic spray nozzle assembly 16 as an atomizing gas as described above, or air, or a combination of inert gas and air, which creates a combustion atmosphere within the drying chamber. If not generated, it may be supplied to the electrostatic spray nozzle assembly 16 as an atomizing gas. Operation of the drying system shown in FIG. 25A is otherwise the same as previously described.

[0134] Referring to FIG. 25B, dry product is discharged from the lower outlet 19b and exhaust air is discharged from the upper outlet, except that the powder collection cone 18a directs the powder to a conventional cyclone separator/filter bag housing 19a. Another alternative embodiment drying system similar to that described above is shown which is directed from port line 165 and recirculated through condenser 170 , blower 168 , drying gas heater 169 and drying chamber 11 . 25C, an alternative drying system similar to that shown in FIG. 25B but having a fine powder recirculation line 19c between the cyclone separator and filter bag housing 19a and the upper end of the drying chamber 11. An embodiment is shown. The dried fine particles separated in the cyclone separator 19a are recycled to the drying chamber 11 through a fine powder recirculation line 19c to produce a powder having fine particle agglomerates. Again, the system otherwise operates the same as previously described.

[0135] Referring now to Figure 25D, another alternative embodiment in the form of a fluid bed powder drying system is shown. The powder drying system again comprises a cylindrical drying chamber 12 having an impermeable liner 100 concentrically disposed therein, and the charged liquid particles being subjected to effective heating provided by the liner 100 as described above. and an electrostatic spray nozzle assembly 16 for directing to zone 127 . In this case, the conically formed collection vessel section 18b conducts powder from the drying chamber 12 through a conventional type fluidized bed screen separator 19c into the collection chamber 19b. In this embodiment, a plurality of fluidized bed cylindrical filter elements 160b, similar to those described in connection with the embodiment of FIG. Supported by Blower 168, in this case, draws air from exhaust plenum 164b, filters out powder and particulate matter therefrom, directs it through condenser 170 and heater 169 via line 165, and into the bottom collection chamber. 19b and recirculated upward through the drying chamber 12. Filters 16b also have respective air control valves 167c for periodically directing pressurized air to and through filters 16b to clean accumulated powder from filters 16b, see US Pat. 8,876,928 with a backflow pulse air filter cleaning device 167b of the type disclosed in U.S. Pat.

[0136] The impermeable liner 100 of the above embodiments is preferably made of a flexible, non-conductive material such as plastic, but alternatively is made of a rigid plastic material as shown in FIG. 3D. You can also In that case, a suitable non-conductive mounting standoff member 100d can be provided to concentrically secure the liner within the drying chamber 12 . Alternatively, as shown in FIG. 3C, the permeable liner is made of a permeable filter material 100b that allows air to flow through the liner for evacuation and a portion, such as one diametric side, of the opposite side. A portion, such as on the side diameter side, can be made of an impermeable material 100a that prevents dry particles from being drawn into the liner.

[0137] Yet another alternative embodiment is illustrated for use in spray cooling molten flow streams such as waxes, hard waxes, and glycerides into a cooling gas stream to form solidified particles. A conventional spray drying system can be easily modified as shown in FIG. 15A. Similar items to those described above are given similar reference numbers. During spray cooling, a feedstock having a melting point slightly above ambient conditions is heated and placed in a holding tank 130, which in this case is encased within insulation 130a. The feedstock is pumped through feed line 131 to atomization nozzle 16 using pump 132 . The molten feedstock is again atomized using compressed gas such as Nitrogen-150. During spray cooling, the molten liquid feedstock may or may not be charged. In the latter case, the electrodes of the electrostatic spray nozzle assembly are de-energized.

[0138] During spray cooling, the atomizing gas heater 152 is turned off and cooled atomizing gas is delivered to the atomizing nozzle 16. During spray cooling, the dry gas heater 169 is also turned off and the dry gas cooled by the dehumidification coil 170a is delivered to the drying chamber 12 through the dry gas line 165. As the atomized droplets enter the dry gas zone 127, the atomized droplets solidify to form particles that enter the collection cone 18 and collect chamber 19 as the gas stream exits for recirculation. collected within. The removable liner 100 can be removed and discarded, again facilitating cleaning of the drying chamber. The insulating air gap 101 prevents the drying chamber 12 from becoming too cold and forming condensation on the outer surface.

[0139] In carrying out yet another feature of the present embodiment, the spray system 10 provides a warning signal in the event of a continuous dielectric breakdown, while providing a continuous electrical field breakdown of the system in the event of a momentary electrical field breakdown within the drying chamber. It can operate with an automatic disaster recovery system that enables operation. A flow diagram for a method of operating the voltage generator fault recovery method used in the spray system 10 is shown in FIG. The illustrated method can operate in the form of a program or set of computer-executable instructions that are executed within controller 133 (FIG. 15). According to the illustrated embodiment, the method shown in FIG. 26 activates or otherwise initiates a liquid pump at 300 to provide a supply of pressurized fluid to the injector inlet. . At 302, a verification is made whether the voltage supply is active. If it is determined at 302 that the voltage supply is not inactive, then at 304 an error message is provided at the machine interface and an existing fault that would have deactivated the voltage supply as determined at 302 has been corrected. The voltage generator and liquid pump are deactivated at 306 until done.

[0140] When it is determined at 302 that the voltage supply is active, at 308 a delay of a predetermined time, for example 5 seconds, is used before the liquid pump is started, and after the delay expires 310 Run the liquid pump at . A check is performed at 312 for a short or arc at 312 while the pump continues to run at 310 . Once a short circuit or arc is detected at 312, an event counter and also an Hold a timer. These checks are determined at 314 each time a short or arc is detected at 312 . When fewer than a predetermined number of shorts or arcs occur within a predetermined period of time, or even a single short circuit or arc is detected, liquid pumping is stopped at 316 and the voltage generator generating the voltage is switched off, e.g. , and after a delay at 308, the liquid pump is restarted at 310 so that the system can correct the fault that caused the spark or arc and continue operation. However, if more than a predetermined number of sparks or arcs occur within a predetermined period of time at 314, an error message is generated at the machine interface at 320 and the system shuts down the voltage generator and liquid pump at 306. Enter standby mode.

[0141] Accordingly, in one aspect, a method of correcting a fault in an electrostatic spray drying system includes initiating a pump start-up sequence that first determines the state of a voltage generator, This involves not allowing the liquid pump to turn on while the device is not yet activated. To accomplish this, in one embodiment, a time delay is used before the liquid pump is turned on to allow sufficient time for the voltage generator to run. The liquid pump is then started and the system continuously monitors for the presence of sparks or arcs, for example by monitoring the current drawn from the voltage generator while the pump is running. When a fault is detected, the voltage generator is turned off, the fluid pump is turned off, and depending on the severity of the fault, the system either restarts automatically or requires operator attention to restart the system. and enter standby mode requiring action.

[0142] Finally, in carrying out further aspects of the present embodiment, the spray-drying system 10 provides controlled and selective aggregation of the spray particles for specific spray applications and final uses of the dried product. It has a control that allows the charging of the liquid sprayed by the electrostatic spray nozzle assembly to be varied periodically in a provocative manner. In one embodiment, selective or controlled agglomeration of aerosol particles is achieved, for example, by combining high and low activation frequencies to produce aerosol particles of different sizes that can result in varying degrees of agglomeration. This is accomplished by varying the time and frequency of spray activation using a pulse width modulated (PWM) injector command signal between . In another embodiment, selective and controlled coalescence of atomized particles can be achieved by modulating the level of voltage applied to charge the atomized fluid. For example, the voltage can be selectively varied in a range such as 0-30 kV. In these voltage changes, the higher voltage applied to charge the fluid generally reduces the size of the droplets, thus acting to reduce the drying time, and furthermore, the carrier is deposited on the outer surface of the droplets. , thus improving encapsulation. Similarly, decreasing the applied voltage tends to increase the droplet size, which can aid coalescence, especially in the presence of small droplets or particles.

[0143] Other possible embodiments that may selectively affect the coalescence of the spray particles include selectively varying over time or pulsing between predetermined high and low values, the Including various other operating parameters. In one embodiment, the atomization gas pressure, fluid delivery pressure, and atomization gas temperature can be varied to control or affect the particle size as well as the drying time of the droplets overall. Additional embodiments may further include varying other parameters of the atomizing gas and/or drying air such as respective absolute or relative water content, water activity, droplet or particle size, etc. . In one particular possible embodiment, the dew point temperature of the atomizing gas and drying gas is actively controlled, and in another embodiment the volume of atomizing gas and/or drying air or the amount of incoming air is also actively controlled. controlled.

[0144] A flow diagram for a method of modulating the pulse width in an electrostatic spray nozzle to selectively control the coalescence of spray particles is shown in FIG. According to one embodiment, the voltage generator is turned on at 322 at the beginning of the process. At 324, a determination is made whether PWM control to selectively control aggregation is active or desired. If PWM is not desired or active, the process controls the system at 326 by controlling the voltage generator to the voltage set point and the fluid ejector is operated normally. When PWM is desired or active, the system alternates between low and high PWM settings for a predetermined period and cycle time. In the illustrated embodiment, this is accomplished by controlling the low pulse period at 330 to a low PWM setpoint at 328 . When the low pulse period expires, the system switches to the high PWM setpoint at 332 until the high pulse period expires at 334 and returns to 324 to determine if another PWM cycle is desired. Although changes in PWM setpoints are described herein in connection with the flow diagram shown in FIG. 27, other parameters can be modulated in addition to or instead of the spray PWM. As mentioned above, other parameters that can be used include the level of voltage applied to alter the liquid, atomization gas pressure, liquid delivery rate and/or pressure, atomization gas temperature, atomization gas and/or drying. These include the moisture content of the gas and/or the volume of atomizing gas and/or dry air or the amount of incoming air.

[0145] Thus, in one embodiment, agglomeration of the spray particles is controlled by varying the duration of the spray. At high frequencies or high PWM, the spray opens and closes more quickly to produce smaller particles. At low frequencies or low PWM, the spray opens and closes more slowly to produce larger particles. As the larger and smaller particles pass through the dryer in alternating layers, regardless of their repulsive charges, some physically interact, bond with each other, and cooperate to produce agglomeration. The specific sizes of the larger and smaller particles, and also the respective number of each particle size generated per unit time, can be adjusted to suit each specific application by adjusting the respective high and low PWM setpoints, as well as It can be controlled by the system by setting a period for each.

[0146] According to yet another feature, in a modular design as shown in Figures 28 and 29, the drying chamber 11 and electrostatic Multiple powder treatment towers 10 having spray nozzle assemblies 16 may be provided. In this case, multiple treatment towers 10 are arranged adjacent to each other around a common work platform 341 accessible at the top by stairs 342 and having a control panel and operator interface 344 located at its end. provided to The treatment towers 10 in this case each include a plurality of electrostatic spray nozzle assemblies 16 . As shown in FIG. 28, eight substantially identical processing towers 10 are provided in which powders are fed via a common powder conveyor 340, such as screw feed, pneumatic, or other powder transfer. Dispense into collection container over means.

[0147] Such a modular processing system has been found to have a number of important advantages. First, it is a scalable processing system that can be tailored to user requirements using common components, namely substantially identical processing powder processing towers 10 . The system can also be easily expanded to have additional modules, as shown in FIG. The use of a modular configuration of the treatment tower 10 allows for a lower building height compared to standard large production spray drying systems that are 40 feet and higher in height and require special building layouts for installation. It also allows the handling of larger volumes of powder with requirements (15-20 feet). The modular design also allows for the isolation and servicing of individual process columns of the system during processing without interrupting the operation of other modules for maintenance. A modular configuration also allows the system to be scaled for energy usage in specific user manufacturing requirements. For example, 5 modules may be used for one processing requirement and only 3 for another batch.

[0148] Referring to Figures 31-33, an alternative embodiment of a powder collection system 350 configured to protect the finished product from being compromised by exposure to moisture, heat, and/or oxygen. It is shown. More specifically, the powder collection system 350 includes a gas blanket system that serves to protect the finished powder from exposure to moist gases, heat, and oxygen associated with the drying process. As shown in FIG. 31, and for example similar to the embodiment of FIG. A powder collection cone 354 relies on the lower end of an isolation plenum 356 . Isolation plenum 356 communicates with drying chamber 358 . Drying gas and powder (generally indicated by arrow 359 in FIG. 31) enter isolation plenum 356 from drying chamber 358 as shown in FIG. Separation plenum 356 also communicates with an exhaust gas outlet 360 through which dry wet gas exits separation plenum 356 while powder falls into collection cone 354 . In this case, collection container 352 is configured as a removable container that is removably secured to the open lower end of powder collection cone 354 by clamp 362 .

[0149] An adapter 364 is provided at the upper end of the collection vessel 352 to facilitate the introduction of blanket gas into the collection vessel 352. As shown in FIG. In the illustrated embodiment, the adapter 364 includes a rubber seal 366 that engages an upper edge 368 of the collection container 352, as shown in FIG. Adapter 364 surrounds the upper end of collection container 352 and defines a central passageway 370 through which dry product can pass from powder collection cone 354 to collection container 352 . In this case, the adapter 364 also defines a flange 372 that is captured by the clamp 362 that secures the collection container 352 to the powder collection cone 354 . A blanket gas inlet orifice 374 communicating with the interior of collection vessel 352 is provided near the top end of collection vessel 352 , in this case in the side wall of adapter 364 . This orifice 374 may be connected to a blanket gas supply such that the blanket gas may be directed inside the collection vessel 352 . The blanket gas may be any suitable gas, preferably cold and without appreciable amounts of moisture or oxygen. Nitrogen is one example of a suitable blanket gas, but other gases or gas mixtures may be used.

[0150] An exemplary blanket gas supply system 378 that can be used to direct the blanket gas to the inlet orifice 374 and thus to the collection vessel 352 is shown in FIG. The illustrated blanket gas supply system 378 comprises a blanket gas supply 380 , which may be a pressurized storage tank, communicating with inlet orifice 374 via gas supply line 382 . An adjustable flow control device 384, such as a flow meter or rotameter, may be provided in gas supply line 382 to control the flow of blanket gas. Flow controller 384 may be configured to be manually adjustable by the operator of the spray drying system, or may be automatically adjustable based on signals received from a controller, for example. A pressure relief valve 386 may be placed in the gas supply line between the flow controller 384 and the collection vessel 352 to prevent over pressurization of the collection vessel 352 and/or the gas supply line 382 .

[0151] In operation, material is spray dried in the drying chamber 358 and falls via gravity and gas flow downward into the separation plenum 356 and then into the collection cone 354. The dropped finished product is then collected in collection container 352 . The blanket gas is introduced into the collection vessel 352 through the inlet orifice 374 to remove the falling product (referenced as 388 in FIG. 32) and the settling product (referenced as 390 in FIG. 32) within the collection vessel 352. cover. The blanket gas slightly pressurizes the collection vessel 352 and adapter 364, thereby preventing the exhausted dry gas from entering the collection vessel 352 and exposing the finished product to the detrimental effects of moisture, heat, and/or oxygen. prevent. Excess blanket gas travels upward through powder collection cone 354, enters separation plenum 356, mixes with the dryer exhaust gas, and exits the drying chamber through exhaust gas outlet 360. Flow controller 384 may be set so that a sufficient flow of blanket gas is directed into collection vessel 352 to protect the finished powder from heat, moisture, and oxygen coming from drying chamber 358 and isolation plenum 356. . However, the blanket gas flow should be kept below a level at which the finished powder will fluidize and become suspended. The blanket gas flow should also be set so as not to pressurize the collection vessel 352 to the extent that dried product is prevented from falling downward into the collection vessel 352 . If desired, the collection container 352 can be removed from the collection cone 354 to remove the finished product. In doing so, a closure mechanism, such as a conventional cap or lid, can be placed over the open top end of collection container 352 to prevent exposure of the product to ambient air, which may contain moisture and oxygen. .

[0152] A further embodiment of a spray dryer configured as a spray cooling system 400 for spray cooling melt stream streams such as waxes and polymers that are solid at or near atmospheric conditions is shown in FIGS. It is The spray cooling system 400 of FIGS. 34 and 35 is configured to discharge a molten feed material into a cold or cooled gas flow stream within the drying chamber 12 of a spray dryer to form solid particles. The spray cooling system 400 of FIGS. 34 and 35 has some similarities to the embodiment of FIG. 15A, and like items to those described above are given like reference numerals.

[0153] According to one important aspect of this embodiment, the spray cooling system 400 of FIGS. More specifically, pulsed spray nozzle assembly 402 is configured to produce a pulsed flow that alternates between on-flow and off-flow conditions. A cross-sectional view of an exemplary embodiment of a suitable pulsed spray nozzle assembly 402 is shown in FIG. The spray nozzle assembly 402 of FIG. 35 is electrically actuated and comprises a nozzle body 404 having a spray tip 406 defining a discharge orifice 407 fixed at its downstream end and a metal plunger 408 disposed within a solenoid coil 410. Prepare. Solenoid coil 410 is contained in a suitable conduit 412 extending from nozzle body 404, in this case suitably coupled to an external power source by electrical conductors. In a known manner, electrical actuation of solenoid coil 410 is effective to move valve plunger 408 to the spray tip open position against the biasing force of closing spring 414 . When in the open position, molten material entering through inlet port 416 of nozzle body 404 may pass through nozzle body 404 and be expelled from the nozzle through spray tip 406 . When the solenoid coil 410 is deactivated, the closing spring 414 moves the valve plunger 408 to the spray tip closed position, blocking the flow of molten material from the spray tip 406 . Such electrically operated spray nozzle assemblies can be rapidly cycled between open and closed positions to intermittently eject a stream of melt flow.

[0154] The illustrated spray nozzle assembly 402 is heated to help maintain a desired high temperature of the molten feed material up to the point at which the material is expelled from the spray tip 406. FIG. Further, the illustrated spray nozzle assembly 402 is configured so that the spray tip 406 can be removed from the nozzle body 404 and replaced with another similarly or differently configured spray tip. The spray tip 406 of the spray nozzle assembly 402 is preferably configured to produce a fan-shaped discharge pattern, which may help prevent particle impingement as the particles are spray cooled. However, depending on the application, feedstock physical properties, and chemistry or morphology requirements, full cone or hollow cone discharge patterns may be used. If a fan pattern is used, multiple spray nozzles arranged such that the straight portions of the fan pattern are parallel to each other may be used. In such a configuration, the on/off function of each individual spray nozzle may be synchronized with adjacent nozzles to help prevent droplet impingement. The ability to change the spray tip 406 on the nozzle body 404 may allow the spray nozzle assembly 402 to produce different spray angles and droplet sizes depending on, for example, the application and/or feedstock material used. In the illustrated embodiment, nozzle body 404 and spray tip 406 are configured to produce hydraulic atomization of molten material. In other embodiments, pulsed spray nozzle assembly 402 may be configured to provide air atomization of the melt stream.

[0155] The pulsed spray nozzle assembly 402 is of a commercially known type, such as those offered under the trade name PulsaJet® by Spraying Systems Co., the assignee of the present application. may be of The various components of the illustrated spray nozzle assembly 402 and their modes of operation are similar to those described in U.S. Pat. No. 7,086,613, the disclosure of which is incorporated by reference. incorporated herein. Alternatively, any spray nozzle assembly capable of producing a pulsed atomization action and configured to stop flow from the nozzle and then deliver full pressure to the nozzle tip as soon as flow resumes can be used. can.

[0156] As in the embodiment of Figure 15A, during the spray cooling operation, the drying gas delivered to the drying chamber 12 is cooled by a chiller, such as, for example, a dehumidification coil. As the atomized droplets expelled from the pulsed spray nozzle assembly 402 enter the dry gas zone 127, the atomized droplets solidify to form particles that enter the collection cone 18 and the gas stream is released for recirculation. As it exits it is collected in the collection chamber 19 . The removable liner 100 can be removed and discarded, again facilitating cleaning of the drying chamber. An insulating air gap 101 may be provided to prevent the drying chamber 12 from becoming too cold and forming condensation on the outer surfaces.

[0157] To ensure that the molten feedstock remains at the desired temperature up to the point of being discharged into the spray dryer, the spray cooling system 400 may, for example, cool the molten feedstock supplied to the spray nozzle assembly 402 to the desired temperature. It can be configured with a heated recirculation loop that can be maintained at high temperatures. An embodiment of such a recirculation loop is shown in FIG. The illustrated recirculation loop includes a heated liquid holding tank 420 that stores molten material. The holding tank 420 is fed by both a supply line 422 communicating with an inlet port 416 of the spray nozzle assembly 402 and a recirculation line 424 communicating with a recirculation port 426 of the spray nozzle assembly (shown schematically in FIG. 34). Connected to nozzle assembly 402 . A temperature sensor 428 located in the feed line 422 near the spray nozzle assembly 402 communicates with and activates the heater 430 in the holding tank 420 so that the molten material is maintained at a desired temperature, e.g., just above the melting point. Control. Maintaining the molten material just above its melting temperature reduces the amount of heat transfer required to convert the droplets of molten material into particles within the drying chamber 12 so that the droplets are formed as quickly as possible. Helps ensure solidification.

[0158] A high flow rate can overwhelm the heat capacity of the drying gas and lead to improper droplet formation. The pulsing action produced by the spray nozzle assembly 402 eliminates high flow rates and allows full pressure delivery of the molten material, which can help ensure proper droplet formation. In addition, pulsing the spray nozzle assembly 402 prevents over- or under-ejection of molten material, which can also result in poor droplet formation.

[0159] A pump 432 is provided in the supply line 422 to move the molten material from the holding tank 420 to the spray nozzle assembly 402. As shown in FIG. In this case, the pump 432 is driven by a variable speed drive 434 that allows the pressure delivered by the pump 432 to be adjusted. Other adjustable drive mechanisms for pump 432 can also be used. A pressure sensor 436 located near the spray nozzle assembly 402 on the supply line 422 monitors the pressure of the molten material and this information is communicated to a variable speed drive 434 which causes the pump 432 to push the molten material to the spray nozzle at a constant pressure. It may be used to secure the supply of the assembly. A heated recirculation loop allows precise control of the temperature of the molten material up to the spray nozzle assembly, including ensuring that the molten material remains at the desired temperature even when the spraying action is interrupted. be In such cases, the heated recirculation loop ensures that the molten material is at the desired temperature for optimum system performance immediately after spraying resumes.

[0160] From the above, it can be seen that a spray drying system is provided that is more efficient and versatile in operation. Because of the improved drying efficiency, spray drying systems are smaller in size and more economical to use. Electrostatic spray systems are also effective in drying different product lots without cross-contamination and are easily modifiable in both size and processing technique for specific spray applications. Spray drying systems are also less susceptible to electrical failures and dangerous explosions from fine powders in the drying chamber atmosphere. The system can also be selectively operated to form particles that aggregate into a form that is easier to use later. The system further includes an exhaust gas filtration system to more effectively and efficiently remove airborne particulate matter from the drying gas exiting the dryer, which system hinders operation and requires costly maintenance. including automatic means for removing the build-up of dry particulate matter on the filter. In addition, the system can be equipped with a gas blanket system to protect the collected finished product from exposure to moist gases, heat, and oxygen from the drying chamber. Moreover, the system is relatively simple in construction and suitable for economical manufacture.

Claims (17)

an elongate body supported in an upright position and defining a drying chamber therein ;
an upper closure mechanism at the upper end of the elongated body and having a dry gas inlet and a lower closure mechanism at the lower end of the elongated body;
a supply of liquid to be spray dried;
An electrostatic spray nozzle assembly supported by said upper closure mechanism , said nozzle body having a liquid inlet and a discharged spray at a downstream end of said nozzle body for directing liquid to be dried into said drying chamber. a tip assembly; and an electrode for connection to a power source for charging liquid entering the drying chamber through the spray nozzle assembly, the liquid supply supplying liquid to be dried to the electrostatic spray nozzle assembly. an electrostatic spray nozzle assembly coupled to the liquid inlet for supplying to
a heated dry gas supply coupled to the dry gas inlet for directing heated dry gas into the drying chamber;
1. A spray drying system for drying a liquid to a powder, comprising:
A closing mechanism at the lower end comprises a powder collection container for collecting powder dried in the drying chamber , the upper end communicating with the drying chamber, and the heated drying gas. a supply of cold blanket gas , wherein said powder collection vessel comprises a blanket gas inlet at an upper end of said powder collection vessel , said blanket gas supply being more sensitive than said heated dry gas. Directing a blanket gas, which is at a lower temperature, across the upper end of the collection vessel and above the dried powder in the collection vessel to prevent entry of the dry gas into the collection vessel and a blanket gas for covering the powder in the body collection container thereby shielding the powder in the collection container from exposure to heat, moisture and oxygen of the heated drying gas from the drying chamber; A spray drying system coupled to the inlet . 2. The spray drying system of claim 1, further comprising a blanket gas supply system interposed between said blanket gas inlet and said blanket gas supply. 3. The spray drying system of claim 2, wherein the blanket gas supply system comprises an adjustable flow controller configured to regulate the flow rate of the blanket gas from the blanket gas supply to the blanket gas inlet. . 4. The spray drying system of claim 3, wherein said blanket gas supply system further comprises a safety valve interposed between said flow controller and said blanket gas inlet. 2. The spray drying system of claim 1, wherein the blanket gas does not contain appreciable amounts of moisture or oxygen. 2. The spray drying system of claim 1, wherein said blanket gas is nitrogen. The powder collection container is an adapter positioned at the upper end of the powder collection container with the blanket gas inlet positioned in a side wall of the adapter to detach the powder collection container from the elongated body. 2. The spray drying system of claim 1, comprising an adapter configured to attach to. an elongated body supported in an upright position;
Closure mechanisms at opposite upper and lower ends of the elongated body for forming a drying chamber within the elongated body, comprising:
a closure mechanism, one of the closure mechanisms comprising a dry gas inlet for introducing cooled dry gas into the drying chamber;
a spray nozzle assembly supported on one of the closure mechanisms, comprising:
an on-flow nozzle body having a liquid inlet for coupling to a feed of molten feed material and a discharge spray tip assembly at a downstream end for directing said molten feed material into said drying chamber; a spray nozzle assembly configured to generate a pulsed flow of said molten feed material that alternates between a state and an off-flow state;
1. A spray drying system for drying a liquid to a powder, comprising:
A spray drying system, wherein the closing mechanism at the lower end comprises a powder collection container for collecting powder dried in the drying chamber . 9. The spray drying system of Claim 8 , further comprising a chiller for cooling the drying gas supplied to the drying gas inlet. 9. The spray drying system of Claim 8 , wherein the spray nozzle body is configured to be electrically actuated between open and closed positions to produce a pulsed flow of the molten feed material. 9. The spray drying system of claim 8 , wherein the ejection spray tip assembly is configured to produce a fan-shaped ejection pattern. 9. The spray drying system of claim 8 , further comprising a heated liquid holding tank in communication with the liquid inlet of the spray nozzle assembly for storing the molten feed material. 13. The spray drying system of claim 12 , wherein the heated liquid holding tank directs molten material to the liquid inlet of the spray nozzle assembly by a feed line. 14. The heating liquid holding tank of claim 13 , wherein the heating liquid holding tank communicates with a recirculation port of the spray nozzle assembly by a recirculation line for recirculating molten feed material from the spray nozzle assembly to the heating liquid holding tank. spray drying system. 15. The spray drying system of claim 14 , wherein a temperature sensor is located in said supply line for communicating with and controlling a heater in said heated liquid holding tank. 16. The spray drying system of Claim 15 , further comprising a pump in said supply line for moving said molten material from said heated liquid holding tank to said liquid inlet of said spray nozzle assembly. 17. The spray drying system of Claim 16 , further comprising a pressure sensor in said supply line in communication with the variable drive of said pump.

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